PDO Prepared statement returns no Results - php

Question

function db_execute($sql,$db,$array)
{
require(getcwd() . '/config/config.php');
if (empty($array))
{
$array = "";
print "Something wrong";
}
$connection = db_connect($db_host,$db_username,$db_password,$db);
$q = $connection->prepare($sql, array(PDO::ATTR_CURSOR => PDO::CURSOR_FWDONLY));
$q ->execute(array($array));
if(!$q)
{
die("Error! " . $connection->errorInfo());
}
$result = $q -> fetchAll();
return $result;
}
$sql = "SELECT VALUE FROM users WHERE :id = :idnum";
$array = array(':id' => 'USER_ID', ':idnum' => '2');
printFormattedArray($array);
printFormattedArray(db_execute($sql,"user_db",$array));
For some reason I can't get any results from this function to return any results. But when I substitute the query with
$sql = "SELECT VALUE FROM users WHERE USER_ID = 2";
It gives me the required results. What am I doing wrong?

Answer 1

Basically, you have 2 choices.
.1. Refrain from using dynamical identifiers in your queries.
So, go for your second query.
$sql = "SELECT VALUE FROM users WHERE USER_ID = :idnum";
$array = array(':idnum' => '2');
$data = db_execute($sql, $array);
.2. If you need dynamical identifiers, you need a distinct placeholder for them as well
So, your code would be like
$sql = "SELECT VALUE FROM users WHERE ?n = ?i";
$data = db_execute($sql, 'USER_ID', 2);
Also,
never connect in the query execution function. Connect once and then use opened connection
always set your PDO to report mysql errors
add this code after connect
$connection->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );